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Freed-memory guard is used to detect UAF (Use-After-Free) memory issue which is illegal access to memory which has been freed. The principle behind is similar to pool guard feature, that is we'll turn all pool memory allocation to page allocation and mark them to be not-present once they are freed. This also implies that, once a page is allocated and freed, it cannot be re-allocated. This will bring another issue, which is that there's risk that memory space will be used out. To address it, the memory service add logic to put part (at most 64 pages a time) of freed pages back into page pool, so that the memory service can still have memory to allocate, when all memory space have been allocated once. This is called memory promotion. The promoted pages are always from the eldest pages which haven been freed. This feature brings another problem is that memory map descriptors will be increased enormously (200+ -> 2000+). One of change in this patch is to update MergeMemoryMap() in file PropertiesTable.c to allow merge freed pages back into the memory map. Now the number can stay at around 510. Cc: Star Zeng <star.zeng@intel.com> Cc: Michael D Kinney <michael.d.kinney@intel.com> Cc: Jiewen Yao <jiewen.yao@intel.com> Cc: Ruiyu Ni <ruiyu.ni@intel.com> Cc: Laszlo Ersek <lersek@redhat.com> Contributed-under: TianoCore Contribution Agreement 1.1 Signed-off-by: Jian J Wang <jian.j.wang@intel.com> Reviewed-by: Star Zeng <star.zeng@intel.com>
EDK II Project
A modern, feature-rich, cross-platform firmware development environment for the UEFI and PI specifications from www.uefi.org.
Contributions to the EDK II open source project are covered by the TianoCore Contribution Agreement 1.1
The majority of the content in the EDK II open source project uses a BSD 2-Clause License. The EDK II open source project contains the following components that are covered by additional licenses:
- AppPkg/Applications/Python/Python-2.7.2/Tools/pybench
- AppPkg/Applications/Python/Python-2.7.2
- AppPkg/Applications/Python/Python-2.7.10
- BaseTools/Source/C/BrotliCompress
- MdeModulePkg/Library/BrotliCustomDecompressLib
- OvmfPkg
- CryptoPkg/Library/OpensslLib/openssl
The EDK II Project is composed of packages. The maintainers for each package are listed in Maintainers.txt.